Many modern electronic devices include touch-sensitive screens (referred to as “touch screens”), which represent graphical displays that receive input through contact with users' fingers, styluses, or other input mechanisms. In a conventional capacitive touch screen, a person's finger or other object serves as a floating plate between two electrodes. Electrical coupling between the electrodes caused by the object can be detected and used to determine the location of the object on the touch screen. These types of systems can detect actual physical contact with a touch screen, and some systems can even detect when an object is very close to the surface of a touch screen (such as within one or two centimeters of the touch screen).
Longer-range or far-field electric field detection systems can be used to detect the presence of a person or other object at farther distances (such as one to two feet). These types of systems typically have a much lower resolution than conventional touch screens. In order to provide both capacitive touch screen sensing and electric field sensing in the same conventional device, the device would require one system for capacitive touch screen sensing and a separate system for electric field sensing.